Copper Poisoning of Sheep

Sheep Diseases

Copper Poisoning of Sheep

Chronic copper poisoning is increasing, due in part to the increasing number of housed sheep and increased over-supplementation

There are two types of copper poisoning; acute poisoning, which is caused by copper treatment for the prevention of copper deficiency, and chronic poisoning, which is caused by the accumulation of copper in the liver due to intake of copper from the diet. Chronic copper poisoning is far more common. Sheep have a remarkable capacity to store copper in the liver, but should a ‘crisis’ occur, massive amounts of copper are released from the liver into the bloodstream. This results in the rupture of red blood cells leading to severe anaemia and jaundice which is rapidly fatal.

There is no specific antidote to copper poisoning, and the condition causes much distress and is usually lethal once clinical signs are present. The diet has to be changed immediately to prevent further cases.

The Risks

Copper poisoning is a common cause of poisoning although the predisposing causes of the ‘crisis’ are not fully understood. It is thought that stressful situations, such as transportation, rough handling, deprivation of food for a short period or a spell of bad weather may precipitate copper poisoning. Incidence has increased in recent years with the intensification of the sheep industry, increased housing of ewes, increased use of breeds susceptible to copper poisoning, such as the Texel (Woolliams et al., 1992), and the availability of cheap feedstuff high in copper, such as brewers’ grains, and feeding concentrate feeds for inappropriate species, i.e. feeding cattle feedstuffs to sheep.

Housed sheep are at special risk of copper poisoning because concentrates and hay contain higher levels of absorbable copper than fresh forage or root crops. It is therefore prudent to make sure that concentrates and compound feeds for sheep are low in copper. Subclinical toxicity has been recorded in Suffolk and Texel-cross lambs fed diets containing 0.19 mmol (12 mg) Cu/kg DM, a level often exceeded in commercial foodstuffs (Woolliams et al., 1982). North Ronaldsay sheep fed on a diet of terrestrial herbage were found to succumb to copper poisoning, despite a relatively high level of molybdenum (MacLachlan and Johnston, 1982). The Orkney breed also appear to be susceptible (Wiener et al., 1977)

The inclusion of cheap feeds, like distillery by-products, in rations is a problem because they contain high levels of copper. Compound feeds designed for cattle or pigs should never be fed to sheep, because they often contain added copper. Other sources of copper poisoning are: the use of copper sulphate in footbaths and the use of copper to spray areas against snails that transmit liver fluke; copper-containing pesticides and fungicides in orchards where sheep graze; industrial copper waste in rivers and streams; slurry spreading from pig units (Kerr and McGavin, 1991); poultry litter used as fertiliser or feed.

The increased use of more susceptible European breeds like the Texel sheep also increases the risk of copper toxicity (MacPherson et al., 1997; Woolliams et al., 1992). For more on Sheep Breeds click here.

Clinical signs include wandering aimlessly, head pressing and generalised weakness.  As jaundice and anaemia set in, breathing becomes shallower. Urine is often dark in colour due to haemolysis .  Death is rapid. Diagnosis is based on housing and feeding history in combination with clinical signs and post mortem findings of a pale liver and black kidneys.  Liver copper concentration will confirm diagnosis. (Sargison, 2016).

Methods of Control and Prevention

Copper poisoning is unlikely to occur in under sustainable production conditions as the proportion of concentrate feeds likely to contain high levels of copper will be low. This is particularly true for organic farmers, where legislation restricts the proportion of concentrates to a minor part of the diet. However, feedstuff low in copper must be used in housed flocks (<10ppm), especially where sheep susceptible to copper poisoning are kept. Cheap feeds high in copper, such as distillery by-products, should not be fed to purebred and crossbred sheep susceptible to copper poisoning. Food compounded for other species (Gough, 1991) or which contains the by-products of other species (e.g. poultry litter) must not be fed to sheep. Copper sulphate for snail control should be avoided.

Under circumstances where supplementation is needed to prevent copper deficiency, this should involve veterinary consultation. An accurate diagnosis should be obtained before any treatment or preventive measures are implemented. Only one source of copper should be made available and every effort should be made to avoid causing stress to animals during copper treatment and for a period afterwards. Anthelmintics and any period of food deprivation around the time of copper treatment should be avoided (Henderson, 1990).

There is evidence that the incidence of copper toxicosis in sheep may be controlled by increasing their dietary zinc intake (Bremner et al., 1976).

Treatment

Effective control of copper poisoning in sheep was obtained by subcutaneous injection of Three doses of ammonium tetrathiomolybdate at 3.4 mg/kg bodyweight on alternate days. This caused a substantial reduction in liver copper content and in liver damage and reduced mortality rate in animals that had developed the haemolytic crisis. No adverse side-effects of the treatment were observed (Humphries et al., 1988). Intravenous injection is also effective (Humphries et al., 1986) but less convenient. A combination therapy of tetrathiomolybdate and d-penicillamine (degradation product of penicillin that chelates copper) has also been identified as being useful to maximize copper removal from the body (Gooneratne and Christiansen, 1997).

Fresh seaweed offered to sheep with symptoms of copper toxicity appeared to be therapeutic, leading to a reduction in blood plasma copper level (Wiener et al., 1977).

Copper antagonists such as molybdenum or sulphur can be added to the diet to prevent further liver accumulation (Sargison, 2016).

Good Practice Based on Current Knowledge

•Do not feed excessive levels of concentrate to sheep.
•Do not feed concentrates high in copper levels to sheep, especially to sheep breeds susceptible to copper poisoning and housed sheep.
•Do not feed sheep food compounded for other species.
•Do not use copper sulphate for the control of snails in areas where sheep are grazing.
•When supplementing sheep with copper, make sure only one source of copper is available and avoid stress during copper treatment and for a period afterwards. Avoid anthelmintics and any period of food deprivation around the time of copper treatment.
•If cases of copper poisoning occur, immediately notify the named veterinary surgeon.